The present invention relates to a novel precision apparatus for the treatment of a wafer material by low-temperature gas plasma reaction provided with an automatic handling mechanism of the wafer.
Recent development in electronics industry is very remarkable and the processing technology of electronic parts such as in transistors, ICs, LSIs, super-LSIs and the like is also rapidly growing. In the photo-fabrication of semiconductor substrate as a typical one of such processing technologies, for example, it is a general trend in etching treatment that a dry-etching process by use of a gas plasma is becoming more and more prevalent replacing the conventional wet-etching process by use of an etching solution. Even when a wet-etching process is undertaken for the precision fabrication of a wafer material, a pretreatment by plasma reaction is recommended for improving the wettability of the surface.
All of the prior art apparatuses for such a gas plasma treatment of wafers are designed for batch-wise operation. For example, 10 to 25 wafers in vertical positions mounted on a wafer stand are placed in a plasma reaction tube, the reaction tube is evacuated and filled with the plasma gas, plasma is generated by applying an electric voltage to effect desired etching and the wafers are taken out of the reaction tube as held on the wafer stand.
One of the major problems in the batch-wise apparatus of the prior art as above is the unevenness of the plasma reaction. Namely, etching with the plasma gas can never be very even on all of so many numbers of the wafers positioned over considerable length in the reaction tube bringing about 10% or more of unevenness in the etching by the plasma reaction. Inspite of the efforts to mitigate such an unevenness by the improvement in the shapes of the reaction tubes and the conditions of the reaction, no satisfactory results have been hitherto obtained.
In the batch-wise apparatuses of the prior art in general, on the other hand, the wafers to be treated are sent from the preceding treatment process as mounted on a wafer cassette, from where they are picked up one by one manually with tweezers and mounted on a wafer stand to be placed in the reaction tube. After completion of the plasma treatment, the wafers are again handled manually to be mounted on another wafer cassette to be sent to the succeeding process. It is a large problem in this manner of manual handling in the plasma treatment process that the full automatization in series of the whole wafer processing procedure is heavily interrupted by this plasma treatment step whereas the wafer cassette can be run through all of the other process steps such as coating of the photoresist, exposure to light, development and rinsing. What is still worse, the wafers thus handled manually with tweezers are sometimes marred by scratching or even cracked. A difficulty should also be taken into consideration that large-sized wafers cannot be held with tweezers as in the recent trend that larger and larger wafers are coming into current.